1. Field
The present disclosure relates to an electrolyte for a lithium secondary battery and lithium secondary batteries including the electrolyte, and more particularly to an electrolyte for lithium secondary batteries that may improve lifespan and high rate characteristics of batteries, and lithium secondary batteries including the electrolyte.
2. Description of the Related Art
Lithium ion batteries (“LiB”) have been adopted as power sources for many mobile devices due to their high energy densities and ease of design. Recently, LiBs are being adopted as power supplies for electric vehicles and power storage and thus, the scope of research is being expanded to LiB materials that provide high energy density and long lifespan. Among the LiB materials, electrolyte additives may be used in a small amount and thus, using the electrolyte additives is a method of improving performance without substantially affecting the properties of an electrolyte.
Due to the desire for high energy density, negative electrode active materials having low potential and positive electrode active materials having high potential are used, and thus, electrolytes are exposed to environments prone to decomposition. As such, in the case of graphite negative electrodes, suitable amounts of electrolytes or additives are currently being used to form films on active materials during initial charging to prevent reduction of electrolytes.
However, as positive electrode active materials that are operated at higher voltages are used, the electrolytes are more prone to oxidation on positive electrode surfaces.
However, additives of the related art, which are for forming films on the positive electrode surfaces, are mostly over-charge protectors. In other words, when voltages increase beyond a certain voltage, thick films are formed on the positive electrode surfaces to prevent transfer of lithium ions and thus, prevent a flow of current.
Recently, research results have been reported about substantially decreasing concentrations of additives for preventing over-charging, to form thin films on the positive electrode surfaces, to thereby improve lifespan characteristics. However, because such films are non-polar, lithium ions may not easily pass through the films and thus, desired properties of LiB may be difficult to obtain. Thus the remains a need for an improved electrolyte for a lithium secondary battery.